Sadler



Aug. 1l, 1959 P SADLER DIFFUSION VACUUM PUMPS Filed Dec. 1o, 195e wwwwww w mw Mw um UUS? mvEN-ron PE-ren Samen 3y www, @al am w onza ATToRNEYS United States Patent DIFFUSION VACUUM PUMPS Peter Sadler,Pendleton, England, assignor to N.G.N.

Electrical Limited, Patri'croft, England, a British com- DanyApplieafien December 10, 1956, serial Ne. 621,449

Claims priority, application Great Britain December 9, 1955 7 Claimse(Cl. 230-101) This invention comprises improvements in or relating todiffusion vacuum pumps, and relates to the type of diffusion vacuumpumps wherein vapor of` `a pumping liquid such as an apiezo oil, issuesfrom within a hood across a gap where the gas to be pumped can diffuseinto it. It is known that in dilusion pumps the best dimension of thegap is a function of the vacuum on which the pump is operating, as wellas other factors such as velocity of the vapor of the pumping liquid,but if the gap is correct the capacity of the pump is a function of thesize of the hood, that is to say up the length of its periphery. Toincrease the diameter of thek p-ump beyond a certain point is noteconomical and therefore the capacity of a pump of this kind as'hithertoconstructed is limited to the capacity of the pump of maximum economicalsize.

According to the present invention such a pump is characterised by thefact that the edge of the hood is formed into folds which affordincreased length of lip within given overall dimensions. Preferably thefolds are such that they afford gaps between themselves which are incommunication with the peripheral gap provided between the hood and thesurounding material of the pump.

In a preferred construction, the pump comprises a vertical tubular body,within which is an upstanding central vapor-tube carrying a hood formedby a plurality of little hoods side by side all round it, with gapsbetween them, and each communicating with the central vapor-tube byports passing therethrough.

The following `is a description by way of example of one construction ofpump in accordance Iwith the in- Vention:

In the accompanying drawing:

Figure l is a vertical section through the pump, and

Figure 2 is a horizontal section `in the line 2-2 of Figure l.

The pump body comprises a stout vertical metal tube 11 which is providedwith a flange 12 at the upper end for attachment to the chamber which isto be evacuated. The tube has a closure 13 at its lower end on the'under side of which is secured an electric heating element 14 clampedin place by a plate 15 and nut 16. The lower end of the tube 11 and theheating element 14 are enclosed within a base portion 17 of the pumpwhich is formed from sheet metal and constitutes :a heating chamberwhich conserves and distributes the heat from the element 14, around thetube 11. The upper portion 18 of the tube is turned down thin and iscovered with an outer tube 19 which is sealed to it at each end andforms a water cooling jacket which is provided with an inlet and outlet(not shown in the drawing).

Within the lower end of the tube 11 there is an evaporating vessel 20for apiezo oil. The evaporating vessel 20 is securely united to avapor-tube 21 which extends upwardly from it concentrically with thepump body into the upper portion which is surrounded with the waterjacket 19. Within the vapor-tube 21 there Patented Aug. 11, 1959 ICC isan innervapor-tube 22 of smaller diameter which e'xte'r'idshout-oft/he'evaporating vessel 20 at the bottom upwardly through th'e outervapor-tube 21 into the upper part'of the water-jackete'd space.

The outer vap'rtube 21, just below the level of the water jacket, isdrilled with a number of sets of holes 23 arranged in gro-ups of three,one above another, at intervals :all around its" periphery. Each groupof holes is rcovered by Aa little-hood 24. Each such little hoodconsists of'two triangular side portions and a narrow taperedcentralportion w-lichr touches the centre tube at its upper end landextends outwardly and -downwardly in an inclined `direction until itnearly reaches the tubular wall 18 of the apparatus, but leaves a smallgap 25 between its ylower lip and 'the outer tube. The little hoods 24are arranged side by side all round the vapor-tube with narrow gaps 26between them approximately equal in size to' the width of the gaps 25between the lower edges of the hoods and the inner-wall 18 of the pumpbody. Thus oil'vapors, which are formed in the outer part of thevaporising vessel `20frise through `the vapor-tube 21, issefthrough vtheports v23 in the wall thereof into the spaces within the little hoods 24and then are dehected -downwardly past the lips formed =by the loweredges of the little hoods. They entrain gases which diffuse into themfrom above, not only the `gases which pass through the gaps 25 of theinclined portions of the hoods 24 but also v'gases which pass downthrough the gaps 26 between hood' and hood. This greatly increases theeffective length of the diffusion lips and the efficiency of the PUmP-Below the hood thus formed there is a lateral outlet 281031 vacuum pumpwhich may for example be of the described inv U.S. Specification No.569,005, dated March 2, .1956. l

The vapor-tube 21 extends up above the subdivided or folded hoodconsisting of the parts 24, as just described and at its upper endcarries an enlarged top 29 somewhat like the top of the funnel of alocomotive. This top 29 is located within and spaced slightly from anintermediate hood 30 which is a plain conical hood and which isconcentrically tted to and carried by the top part of vapor tube 22. Thetop 29 is provided with a central circular opening 51 through which thevapor tube 22 passes. The diameter of this opening 51 is greater thanthe outer diameter of the vapor-tube 22 so that there is an annular port52 connecting the interior of the top 29 with the under side of the hood30. Further vapor issues from the vapor-tube 21 through the annular port52 into the hood 30 and thence downwardly to afford an additional stageof pumping action as indicated by arrow 31. The inner vapor-tube 22 isextended upwardly as shown at 33 and terminates within a topmost hood34. At its upper end the vapor-tube 122 has a central port 53 whichplaces the interior of the vaportube 22 into communication with theunderside of the hood 34. The upper hood 34 is smaller and more widelyspaced from the pump casing and affords a preliminary impulse stage anddiffusion lip for the gases which are to be evacuated. A transverse disc35 is mounted above the uppermost hood and is spaced by a small gap fromthe surrounding pump body. Within the topmost hood is an internalscrew-threaded lug and the whole assembly of hoods and vaporisingchamber is held down on to ythe closure at the bottom of the pump bodyby a central screwed rod 36.

If desired, not only the lowermost hood 2.4 can be sub-divided by foldsas above described but also the intermediate or uppermost hoods 30 and34 can lbe so subedivided if desired.

I claim:

l. A diffusion pump comprising in combination an upstanding tubularbody, a vapor tube centrally located within the body, means at thebottom of the vapor tube for producing an upward stream of vaportherein, a hood carried upon the vapor tube constituted by an assemblyof little hoods side by side around the vapor-tube, with narrow parallelgaps between them, each hood communicating with the central vapor tubeby ports passing through said tube, the outer edges of the little hoodsbeing parallel with the inner wall of the tubular body and spacedtherefrom by gaps equal in width to the gaps between the hoods, an inletto the body at the top thereof, an outlet therefrom below the hood, andmeans adjacent the upper end of said vapor-tube for substantiallyobstructing the upward iiow of vapor therefrom.

2. A diffusion pump as claimed in claim 1, wherein the said means forproducing an upward stream of vapor comprises an evaporating vessel inthe lower end of the body, and an electrical heating element in heattransfer relationship with said evaporating vessel.

3. A diffusion pump as claimed in claim 1 further comprising a secondhood carried by the vapor-tube at a higher level than the other hood.

4. A diffusion pump as claimed in claim 2, further comprising an innervapor-tube within the vapor-tube and a furtherphood, the lower end ofsaid inner vaportube being received within said evaporating vessel andthe upper end of the inner vapor-tube extending upwardly into saidfurther hood.

5. A diffusion pump as claimed in claim l, further comprising a hollowbase and a heating element within said hollow base, said hollow baseencasing the lower end of the tubular body and being shaped to conserveand distribute the heat from the heating element.

6. A diffusion pump comprising in combination an upstanding tubularbody, a rst vapor-tube centrally located within `the body, an innervapor-tube centrally located within said first vapor-tube, means at thebot- "tom of said vapor-tubes for producing an upward stream of vaportherein, ports passing through the rst vapor-tube intermediate itslength, a first hood carried by the first vapor-tube and beingconstituted by an assembly of little hoods side by side around thevapor-tube with narrow parallel gaps therebetween, each hoodcommunicating with the interior of the first vapor-tube through theports, the outer edges of the little hoods being parallel wih the innerwall of the tubular body and spaced therefrom by a gap equal in width tothe gaps between the hoods, an intermediate hood carried by said innervaportube intermediate its length, said first vapor-tube terminatingwithin said intermediate hood and in communication therewith through anopening in said first vaportube, an upper hood, the upper end of saidinner vaportube terminating within said upper hood, said upper hoodbeing in communication with the interior of said inner vapor-tubethrough a port in the inner vapor-tube, an inlet to said `tubular bodyat the top thereof and the outlet from said tubular body below said rsthood.

7. A diifusion pump comprising in combination a tubular body, a vaportube centrally located within the body, means at the bottom of the vaportube for producing an upward stream of vapor therein, ports in thevapor-tube, hood means surrounding the vapor tube and in communicationwith the interior thereof through said ports, said hood means comprisinga downwardly sloping exterior wall divided by a series of inwardlyfolded walls, the lower edges of the divided exterior wall being spacedby a gap from `the interior of the tubular body and the inwardly foldedwalls being separated from one another by gaps of closely comparablewidth to the gap between the exterior wall and the body, and meansadjacent the upper end of said vapor tube for substantially obstructingthe upward flow of vapor therefrom.

References Cited in the tile of this patent UNITED STATES PATENTS1,367,865 i Crawford Feb. 8, 1921

